LD-ERROR-ACTION

Ld-error-action is an ld special (see ld). The accessor is
(ld-error-action state) and the updater is
(set-ld-error-action val state). Ld-error-action must be
:continue, :return, or :error. The initial value of
ld-error-action is :continue, which means that the top-level
ACL2 command loop will not exit when an error is caused by
user-typein. But the default value for ld-error-action on
calls of ld is :return.

The general-purpose ACL2 read-eval-print loop, ld, reads forms from
standard-oi, evaluates them and prints the result to standard-co.
However, there are various flags that control ld's behavior and
ld-error-action is one of them. If, while ld-error-triples is t, a
form evaluates to three results, the first of which is non-nil and
the third of which is state, an error is said to have occurred. If
an error occurs, ld's action depends on ld-error-action. If it is
:continue, ld just continues processing the forms in standard-oi.
If it is :return, ld stops and returns as though it had emptied the
channel. If it is :error, ld stops and returns, signalling an error
to its caller.